Trophic Transfer

Trophic Transfer

Trophic transfer received a score of 3. This score includes 3 points to reflect

the high ranking for magnitude of uncertainty. In Tier III, if dredged material

bioaccumulation significantly exceeds bioaccumulation in the reference

sediment, the biomagnification potential of COCs must be considered. However,

no guidance explains how to evaluate this potential impact quantitatively.

Chronic Bioassays

Chronic bioassays received a score of 5, with 2 points for a moderate ranking

for magnitude of uncertainty and 3 points for not accounting for population-level

effects. Although prediction of the environmental impact on the basis of results

of laboratory bioassays is uncertain, chronic bioassay results can be used in

conjunction with demographic models to evaluate the potential for long-term

impacts on populations. Use of quantitative uncertainty analysis and probabilistic

modeling will be critical elements in such an approach.

Assessment and Measurement End Points

Assessment end points and measurement end points were not scored. Like

many other elements of the "Problem Formulation" step in risk assessments,

selection of these end points is primarily a qualitative step. However, there is

significant uncertainty in selecting appropriate assessment and measurement end

points. Often, it is the relationship (or lack thereof) between the assessment and

measurement end points that dominates the uncertainty. An explicit protocol for

selection of appropriate measurement and assessment end points with an

emphasis on a clear connection between the two would reduce the uncertainty

associated with selecting ill-defined measurement and assessment end points.

Fate and Transport Models

To support risk assessments, fate and transport models are needed to provide

estimates of contaminant concentrations at locations where humans and

ecological receptors might contact dredged material contaminants. These models

received no score in this report because many models are available, each with

varying degrees of associated uncertainty.

Chapter 6 Preliminary Ranking and Recommendations